how to finish a broken wad with cheats disabled

[Doohnibor]

Hi,

I am currently playing through an old PSXDoom release on nightmare skill.  Right now I got stuck in the last map "mephisto`s mausoleum". There is a problem with this particular release. After killing all the Mancubi nothing happens and the player is stuck in the inside area with no chance to get out. 

 

I cannot idclip out of the area because nightmare skill has cheats disabled. (turning cheats back on, works only for the next game)  

 

Can anyone think of a way how I can finish the level?